1. Field of the Invention
The present invention relates to an electrostatic latent image developing toner and a manufacturing method thereof. The toner is used to develop an electrostatic latent image in electronic photography, electrostatic recording, and electrostatic printing.
2. Description of the Related Art
In recent years, the manufacturing of toner particles using granulation methods among the wet-type methods represented by emulsion dispersion methods, suspension polymerization methods, and emulsion polymerization methods have become a focus of attention from the perspectives of reducing manufacturing costs while achieving high quality images.
Emulsion dispersion methods involve dissolving or dispersing binder resin and colorant in a suitable organic solvent to obtain a color resin solution, adding this solution to an aqueous liquid medium, and vigorously mixing the fluid to form droplets of resin solution. This material is then heated, to remove the organic solvent from the droplets to achieve granulation.
Suspension polymerization methods involve suspending polymerizable components which comprises polymerizable monomer, and polymerization initiator, colorant and other additive added as necessary in a dispersion medium to form oil droplet dispersion particles, polymerizing the monomer to form colored resin particles (toner particles).
Emulsion polymerization methods involve adding a nearly water insoluble polymerization monomer in water and attaining an emulsion state, then accomplishing granulation by polymerization using a water soluble polymerization initiator. Generally, colorant, charge control agent and the like are added post polymerization and after the particles are formed.
The dispersants used in wet-type granulation include inorganic dispersion agents and organic dispersing agents. Tribasic calcium phosphate is generally used as an inorganic dispersing agent. Since tribasic calcium phosphate effectively produces a pH of 10 to 14 in water, polyester resin is hydrolyzed by these components due to the alkalinity resistance required by the toner particles so as to cause problem at low melt temperatures and the like, and charge controllers which do not have alkalinity resistance disadvantageously loose functionality. For this reason these aspects must be considered when selecting materials, which greatly restricts the materials which can be selected for the toner. Manufacturing conditions also must be controlled because the toner component dispersion density markedly changes particle size and shape depending on the granulation conditions such as oil-in-water (O/W) emulsions and the like.
Toner manufactured by wet-type granulation methods such as emulsion dispersion, suspension polymerization, and emulsion polymerization using organic dispersing agent disadvantageously produce chargeability problems, e.g., generation of inadequately charged particles and many reverse charge toner particles. In particular, chargeability may be greatly reduced or fluctuate due to environmental conditions. This tendency may become pronounced under high temperature, high humidity conditions.
Wet-type granulation methods generally add dispersing agent or emulsifier, but the dispersing agent or emulsifier used for suspension or emulsification is removed by washing in water after granulation.
Conventionally, however, residual dispersing agent and the like adhered to the surface of the toner particles is not completely removed simply by washing in water, and this residual material on the surface of the toner may be a factor affecting toner chargeability. Various proposals have been offered to eliminate the previously described disadvantages, but none have adequately resolved these disadvantages with organic dispersing agents are used.